// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_SUPPORTS_USER_DATA_H_
#define BASE_SUPPORTS_USER_DATA_H_

#include <map>
#include <memory>

#include "base/base_export.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/sequence_checker.h"

// TODO(gab): Removing this include causes IWYU failures in other headers,
// remove it in a follow- up CL.
#include "base/threading/thread_checker.h"

namespace base {

// This is a helper for classes that want to allow users to stash random data by
// key. At destruction all the objects will be destructed.
class BASE_EXPORT SupportsUserData {
public:
    SupportsUserData();

    // Derive from this class and add your own data members to associate extra
    // information with this object. Alternatively, add this as a public base
    // class to any class with a virtual destructor.
    class BASE_EXPORT Data {
    public:
        virtual ~Data() = default;
    };

    // The user data allows the clients to associate data with this object.
    // Multiple user data values can be stored under different keys.
    // This object will TAKE OWNERSHIP of the given data pointer, and will
    // delete the object if it is changed or the object is destroyed.
    Data* GetUserData(const void* key) const;
    void SetUserData(const void* key, Data* data);
    void RemoveUserData(const void* key);

    // SupportsUserData is not thread-safe, and on debug build will assert it is
    // only used on one execution sequence. Calling this method allows the caller
    // to hand the SupportsUserData instance across execution sequences. Use only
    // if you are taking full control of the synchronization of that hand over.
    void DetachFromSequence();

protected:
    virtual ~SupportsUserData();

private:
    using DataMap = std::map<const void*, std::unique_ptr<Data>>;

    // Externally-defined data accessible by key.
    DataMap user_data_;
    // Guards usage of |user_data_|
    SequenceChecker sequence_checker_;

    DISALLOW_COPY_AND_ASSIGN(SupportsUserData);
};

// Adapter class that releases a refcounted object when the
// SupportsUserData::Data object is deleted.
template <typename T>
class UserDataAdapter : public base::SupportsUserData::Data {
public:
    static T* Get(const SupportsUserData* supports_user_data, const void* key)
    {
        UserDataAdapter* data = static_cast<UserDataAdapter*>(supports_user_data->GetUserData(key));
        return data ? static_cast<T*>(data->object_.get()) : NULL;
    }

    UserDataAdapter(T* object)
        : object_(object)
    {
    }
    T* release() { return object_.release(); }

private:
    scoped_refptr<T> object_;

    DISALLOW_COPY_AND_ASSIGN(UserDataAdapter);
};

} // namespace base

#endif // BASE_SUPPORTS_USER_DATA_H_
